Recently, as a solid-state imaging device used for a digital camera, a CMOS (Complementary Metal Oxide Semiconductor) image sensor has been proposed and commercialized. The features of this CMOS image sensor are that it uses a single power supply, operates at a low voltage, and consumes low power.
The pixel sizes of CMOS image sensors have decreased year by year because of demands for larger numbers of pixels and smaller optical sizes. For example, a CMOS image sensor used for a digital camera or the like has a pixel size of about 2 μm to 3 μm. As the pixel size of a CMOS image sensor decreases, the openings between the interconnections through which light passes decrease in size, resulting in a decrease in sensitivity.
In order to solve this problem, a backside illumination image sensor has been developed, which has a signal scanning circuit and interconnection layer (circuit unit) on the upper surface of a semiconductor substrate, and a light-receiving surface on a side (rear surface side) opposite to the circuit unit. Using this structure can increase the sensitivity of the CMOS image sensor.
However, a backside illumination CMOS image sensor has no interconnection layer on the light incident surface side, and hence the semiconductor substrate is located immediately below the color filters. For this reason, light, especially light having a long wavelength, which strikes a given pixel at a certain angle (obliquely strikes the incident surface) propagates to an adjacent pixel without being interfered by the interconnection layer, thus causing crosstalk with the adjacent pixel and color mixing. This degrades color reproducibility on a reproduced picture, resulting in deterioration in image quality.